class_docstr: Represents a config parameter.
  
  A config parameter has a name, a default value, a type,
  a category, a documentation, an optional longer documentatation
  and an optional subtype for list style option.
  
  Most of these informations are used in cabaret to auto generate
  forms representing these options.
docstr: Create a configuration key
docstr_tok: ["Create","a","configuration","key"]
code: def __init__(
      self, default_value, type_, category, doc, subdoc="", subtype=None
  ):
      """Create a configuration key"""
      self.value = default_value
      self.type = type_
      self.doc = doc
      self.category = category
      self.subdoc = subdoc
      self.subtype = subtype
      self.name = "Unbound"
      if category not in self._categories:
          self._categories.append(category)
  
      CONFIG_ITEMS.append(self)
  
imports: from copy import deepcopy
  from pygal import formatters
  from pygal.interpolate import INTERPOLATIONS
  from pygal.style import DefaultStyle, Style
label_desc: Use image node_id 1 to create a new Key object from inherited base classes: object with example: obj = Key(default_value, type_, category, doc, subdoc, subtype)